Conventionally, a liquid crystal display device has been used in a variety of electronic devices such as a television set, a laptop computer, a desktop personal computer, a PDA (personal digital assistant: a mobile terminal), and a mobile phone. The liquid crystal display device has the advantages that it (i) is thinner and lighter than a CRT (Cathode Ray Tube) display device and (ii) consumes less electric power than the CRT (Cathode Ray Tube) display device because the liquid crystal display device can be driven by a lower voltage than the CRT (Cathode Ray Tube) display device.
Particularly, a liquid crystal display device employing TFT (Thin Film Transistor) elements (such a liquid crystal display device is called a TFT liquid crystal display device) achieves high display quality, because all pixels are switched over via respective TFT elements.
Meanwhile, it has become rapidly widespread in an electronic device such as a television receiver that a moving image is displayed by such a liquid crystal display device. Accordingly, the liquid crystal display device has been required to further increase a response speed of a liquid crystal display panel so as to achieve a moving image with higher quality.
In view of the circumstances, an OCB mode liquid crystal display device has particularly attracted attention recently. The OCB mode liquid crystal display device is generally configured such that: a liquid crystal layer is provided between two substrates which have been subjected to an alignment treatment so as to cause liquid crystal molecules to be aligned in a same direction in parallel with one another; wave plates are provided on surfaces of the respective two substrates; and polarization plates are further provided on the respective wave plates so that the polarization plates are in a crossed Nicols relation.
(Reverse Transition)
In a case where the OCB mode is employed in for example a normally white mode (NW mode), in which a black display is carried out while a high voltage is being applied and a white display is carried out while a low voltage is being applied, a voltage applied to the liquid crystal layer needs to be reduced to nearly a critical voltage (Vcr) between splay and bend orientations so that a white display is achieved with high transmittance.
Because of this, a bend-splay transition (reverse transition) sometimes occurs while the white display is being carried out, which allows a display to be no longer properly carried out. Note that the bend-splay transition here means a phenomenon of the liquid crystal molecules, which once have been in a bend orientation state, again returning into a splay orientation state.
The reverse transition occurs even while the drive is being carried out by a voltage equal to or higher than the critical voltage (Vcr). In a case where the liquid crystal display device is the TFT liquid crystal display device, the reverse transition may occur in gaps between pixel electrodes, which gaps are above a gate bus line and above a source bus line. If the reverse transition occurs, a region above the gate bus line and a region above the source bus line, in which regions the liquid crystal molecules are in a splay orientation state (such regions are hereinafter referred to as splay orientation regions), are likely to merge together.
If the splay orientation regions merge together, the play splay orientation regions thus merged may spread into a display region while the white display is being carried out. This causes a display defect.
(High White Voltage)
In order to prevent the reverse transition, there have been proposed a variety of methods.
One of the methods is to increase a voltage, which is applied while the white display is being carried out in the normally white mode (such a voltage is called a white voltage), to a voltage sufficiently higher than the critical voltage (Vcr).
However, with this method of increasing the white voltage, it was difficult to achieve an OCB panel with high brightness, because of trade-off between the white voltage and brightness.
(Black Insertion)
There has been proposed, as another method for preventing the reverse transition, a method in which a signal is applied separately from an image signal so as to prevent a reverse transition.
Specifically, for example, there has been proposed a method of stably maintaining a bend orientation by inserting a black display once or more times per frame of each display image.
However, according to the method of inserting the black display, there has been a problem that white brightness decreases as is the case with the method of increasing the white voltage.
Further, according to the method of inserting the black display, there has been another problem that flicker occurs.
(Patent Literature 1)
Patent Literature 1 discloses a configuration in which salient parts are provided in peripheral parts of pixels so as to allow all the liquid crystal molecules to efficiently transit into the bend orientation state. The salient parts are in a plane parallel with a surface of a substrate. This is described below with reference to a drawing.
FIG. 12 schematically illustrates how a liquid crystal display device 100 disclosed in Patent Literature 1 is configured. As illustrated in FIG. 12, the liquid crystal display device 100 disclosed in Patent Literature 1 includes (i) a plurality of signal electrode lines 106 and (ii) a plurality of gage electrode lines 107 substantially orthogonal to the plurality of signal electrode lines 106.
The plurality of electrode lines 106 and the plurality of gate electrode lines 107 substantially define pixel regions, in each of which a pixel electrode 102 having a substantially rectangular shape is provided. The pixel electrode 102 has a switching transistor 108, which is provided in the vicinity of corresponding one of intersections of the plurality of signal electrode lines 106 and the plurality of gate electrode lines 107.
According to such a liquid crystal display device 100 disclosed in Patent Literature 1, the plurality of signal electrode lines 106 have salient parts 161. Meanwhile, the pixel electrode 102 has, in a portion facing corresponding one of the salient parts 161, a reentrant part 121 which is in a shape corresponding to the shape of the salient part 161.
The pixel electrode 102 also has a salient part 122, which has a shape identical to that of the salient part 161 of one signal electrode line 106 which corresponds to the pixel electrode 102. Meanwhile, the other signal electrode line 106 which corresponds to the pixel electrode 102 has, in a portion facing the salient part 122, a reentrant part 162 which is in a shape corresponding to the shape of the salient part 122.
Patent Literature 1 teaches that this configuration makes it possible to allow all the liquid crystal molecules to efficiently transit into the bend orientation state.
Patent Literature 1
Japanese Patent Application Publication, Tokukai, No. 2002-250942 A (Publication Date: Sep. 6, 2002)